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Building Gravitational Wave Experiment

  1. Feb 5, 2010 #1
    I have recently come up with an idea about trying to build an apparatus to run some gravitational wave experiments. Now I am still a novice so I wrote Professor Scott Hughes about my idea, he provided me with the mathematical equations that basically show the experiment is impossible. I will share with everyone what I have to work with because I want to figure out a work around or maybe I can build this to study methods of transfering momentum or energy. Here is what I am studying courtesy of professor Hughes:

    Mr. Vogeler:

    To get any interesting GW power, the spheres would have to move at a
    significant fraction of the speed of light.

    To set an upper limit, I'll take the spheres to be 2 meters in
    diameter (a bit larger than your 5 feet). I'll take them to be
    filled with mercury (denser than gallium; I'm not suggesting you
    actually do this, just doing the calculation to prove the
    principle). Mercury has a density of a bit less than 14 grams per
    cubic centimeter, so the spheres would each have a mass of about

    M = (4/3) pi (14 grams/cm^3)(100 cm)^3 = 59,000,000 gm

    (At each step I've rounded up slightly, so my calculation will be an
    overestimate.) If I have two "stars" of mass M orbiting one another
    with their centers separated by a distance R and orbiting with a
    period T, then the power generated by gravitational waves is given by

    P = (8/5) (G/c^5) M^2 R^4 (2 pi/T)^6

    (As you'll see in a minute, the factor of G/c^5 --- where G is the
    gravitational constant, and c is the speed of light --- really kills
    us. This is why all GW experiments are based on astrophysical
    sources, where we can get masses that are stellar or larger.)

    For your experiment, M = 5.9 x 10^7 grams. The center to center
    separation R is 200 cm (well, 5 feet --- but I'm rounding up a bit to
    get an overestimate). The period is

    1/(2000 rpm) = 0.005 minutes = 0.03 seconds

    The numerical factor G/c^5 is 2.76 x 10^(-60) sec^3/(gm cm^2). Let's
    put all of this together:

    P = [8/5][2.76 x 10^(-60) sec^3/(gm cm^2)][5.9 x 10^7 gm]^2 [200 cm]^4
    [2 pi/(0.03 sec)]^6

    = [2.76 x 10^(-60)][7.52 x 10^(38)] gm cm^2/sec^3

    = 2.08 x 10^(-21) erg/sec

    Converting to Watts (1 Watt = 10^7 erg/sec), your proposed apparatus
    would generate a gravitational wave power of about 2 x 10^(-28)
    Watts. If we imagine that you can make the rotational frequency go
    arbitrarily high, it would be useful to see how this results scales
    with that frequency:

    P = 2.08 x 10^(-28) Watts (f/2000 rpm)^6.

    Doing a little bit of algebra, we see that if want this to get up to
    1 Watt, we need to dial the frequency up to about 82,000,000
    revolutions per minute. At this speed, the spheres would be moving
    at a speed of about 1,400,000 meters per second --- about 0.5% of the
    speed of light. (Of course, at this speed, the material out of which
    the spheres are made would not be able to hold together. This is why
    astrophysical gravitational wave sources are objects like neutron
    stars and black holes --- their enormous self gravity is what allows
    them to hold together while they whirl about one another at speeds
    which are an appreciable fraction of the speed of light.)

    I'm afraid there's no way to overcome the fundamental limits set by
    that factor of G/c^5 --- you just need enormous masses and enormous
    speeds. Anything you can make on earth will not do the trick.

    Please note I'm going to be away from my email for the holidays and
    am unlikely to answer any followup questions on a short timescale.

    Scott Hughes

    Now I am not satisfied lol. It seems to me we should be able to come up with a way to pull something off.

    First are there any better alternatives than using mercury, materials that would hold together. What about super-fluids it seems to me a super-fluid might be able to be rotated magnetically thus reducing stress on the machine.. maybe it would hold together at these extreme forces. I wish I paid attention during chemistry!!

    Secondly what would be the minimum detectable output power as opposed to hitting 1 watt, I have no idea what kind of equipment would be used to detect this and what its sensitivity could be tuned to.

    Now even if there is absolutely no way around lowering the speed enough and still making it work. What about using the apparatus to study methods of inducing a gravitational wave without the wave itself. It would seem to me the amount of energy needed to set the wave off would be large and easily detectable.. possibly at far lower velocities. So do you believe I could at least use my apparatus to study methods of transferring potential energy into magnetic energy?
  2. jcsd
  3. Feb 5, 2010 #2
    I think there is a typo in his writings. 82E6 rpm corresponds to 1.4e6 revolutions per second, not 1.4E6 m/s? The velocity is 9E6 m/s since the circumference is 2*pi meters if I understood the geometry correctly, so it becomes 3% of the speed of light. At least that is what I got in my (quick) calculation. I might be wrong of course. But this doesn't change any of his conclusions.

    In this rotating state, the system has a kinetic energy of around 5E18 J at 82E6 rpm!

    If I understood the wikipedia figure for the world electricity usage, the power consumtion of the world is on average 2E12W. This means that if you instead redirect all that energy to your two balls, then you would need 30 days to build up the necessary kinetic energy. I'm pretty sure we humans are not able to concentrate that amount of energy in such a limited space... You would need a "similar" energy input independently of how you try to realize your experiment similar to the one you have proposed.

    The centripetal force needed to keep the ball on its circular orbit is around 8E13N, similar to lifting around 1400 Great Pyramids of Giza. This force needs to be applied in an area of the order of 1m^2:

    Another thing, the slower the balls are moving, the smaller is the amplitude of the GW. I think that for any reasonably large enough value of the RPM, this contraption will shake so much (and its surroundings) as to make it impossible to place any measurement apparatus in its vicinity. if you lower the rpm, the GW is weaker, and you get the same problem because the measurement apparatus needs to be more sensible.

  4. Feb 5, 2010 #3
    "your proposed apparatus
    would generate a gravitational wave power of about 2 x 10^(-28)"

    I am wondering how he came up with that. I told him that I could generate 20,000 rpm but I was not sure on velocity as I have not built anything like this. But it would be slow in that regard compared to the rpm.. probably very slow I don't know if I could make it run 100 ms at that size. So whatever he used for velocity there didn't come from actual testing.

    So there is no way at all to generate any measurable gravitational wave. But I still have the ability to study the transfer of potential energy to kinetic energy to magnetic energy right? And wouldn't that be an important step in itself. I mean who knows what kind of effects I can record unless I actually build the thing and start running some tests. I have a setup for the electromagnetic field already in the order of 30,000 dc volts. Its going to be one heck of a magnetic field and it will give tons of great data in that regard.

    I'm not sure if studying transfer of energy would help in the search for GW throughout the cosmos however.

    I have one dynamo together, I didn't built it that large because the weight would be tremendous and I would have to have engines large enough to drive an ocean liner lol. I am going with my original idea of 5 ft diameter 1 1/2 " thick steel. And I am doubting I could use mercury at such a high rpm even with that size thickness. The mount is going to be a piece of engineering, I don't have anything fabricated for it yet but I have some ideas on paper. Getting a strong enough shaft will be hard enough, but its going to be built like an H on its side. The arms that support the dynamos are going to have to be adjustable so I can run the machine at varying distances between the dynamos. This is going to be a challenge for sure even at low speeds. But it should be interesting.
  5. Feb 5, 2010 #4
    His calculation uses 2000rpm, not 20000rpm. Maybe he misread your number. Although that doesn't change is conclusion about the practical feasability. I'm not sure what you mean by transfer potential energy into magnetic energy. You can do that by dropping a charged object from a height. Initially it has gravitational potential energy. When it has gained speed downward, a stationary observed will measure a nonzero magnetic field strength. This is the same thing that happens when electrons move through an electric circuit. Actually in that case, it is the chemical potential energy that is converted into e.g. magnetic energy around the current-carrying wire.

    The problem with gravitational experiments is that the gravitational force is so damn weak! But they have managed to measure the actual gravitational attraction between small dense objects to test the accuracy of Newton's gravitational law on small scales. So far I believe it to be verified experimentally down to distances on the order of 0.1mm, or maybe even a bit smaller now.

    Since it is in fact possible to measure the static gravitational field from a manageable object, it would be possible to measure the varying gravitational field as this object is moved back and forth in front of the detector. But that ain't a gravitational wave :-)

    I think large space-based experiments are the most promising for detecting gravitational waves:

  6. Feb 5, 2010 #5
    Yeah I think he kind of had to rush through that letter. Hes probably busy writing REAL physics lol. But what I mean by transfer of energy is from one dynamo to the other. By varying speed, or say a wobble on one dynamo and monitoring the effect it has on the other. I have some pretty cool magnetic sensors and a pretty good magnetometer.

    What you are telling me about measuring gravitational attraction between objects that size or smaller... that rocks. I bet that test equipment would cost a fortune though. I wonder how they build such a thing... any idea where I can hunt one up ?? lol

    Listen if you guys hear about some hillbilly that crashed a test rig and died of mercury poison you'll know what happened lol :)
  7. Feb 5, 2010 #6
    If you have not seen it, I was refering experiments like this:


    This old experiment is not expensive to do. It uses some steel balls, and measures the ratio of a twisting force to the force of gravity I think. There are some nice graphics there showing the experimental setup. It is probably not so expensive an experiment do to, since it was already done a long time ago. He refered to the experiment as "weighing the world", which is true because he used it to determine the mass of earth! A fantastic experiment, I think.

    The newer experiments to test Newtons law at short distances might be a tad more expensive, but its only peanuts compared to particle physics!

    Anyway, please don't do anything dangerous!

  8. Feb 5, 2010 #7


    User Avatar

    Staff: Mentor

    Here's a description of a homemade version of the Cavendish experiment:

    http://www.sas.org/tcs/weeklyIssues_2005/2005-07-01/feature1/index.html [Broken]
    Last edited by a moderator: May 4, 2017
  9. Feb 6, 2010 #8

    I have just got a reply from Stirling Colgate about my dynamo experiment idea. He sent me his paper about his upcoming dynamo experiment. He has two counter rotating cylinders, one inside the other with end plates keeping the sodium in between the cylinders with empty space in dead center, through that dead center they are shooting a jet of sodium.

    They are experimenting with a simulated model of an accretion disk. Now it appears they think this might be a self sustaining dynamo????? Stirling also told me in his letter he would like to make two of them and set them orbiting each other.

    Guys let me ask you all. Don't you ever doubt predictions about events we have never witnessed? I mean what if the numbers are all wrong and I fire up my machine and launch myself into orbit?? seriously I mean if it ends up that this is really not possible, that gravitational waves are a flop which it may end up. What does that mean for the standard model??

    Also if anyone is interested in this paper The New Mexico alpha-omega Dynamo Experiment:
    Modeling Astrophysical Dynamos
    S. A. Colgate1
    2, V. I. Pariev2
    3, H. F. Beckley1, R. Ferrel1,
    V. D. Romero1, J. C. Weatherall1
    1 Department of Physics, New Mexico Institute of Mining and Technology

    I really am having a hard time understanding this. If someone could summarize this in plain english I would be glad to send you a copy.
  10. Feb 6, 2010 #9
    I'm going to respond to setup portion here first.
    just a quick read thru the proposal and I wonder if these guys have any experience with high rpm engines and torque converters. counter rotating fluid and stators build immense heat. I didn't catch any surface sheer torque from the setup, then again I quickly went thru it. I will say that they are playing with a mortally dangerous setup, the force that will produce if it explodes will be tremendous!

    I may only have hands on engineering experience but I've seen my share of devastation from rpm induced explosions of flywheels and clutch's. the vehicle looks as though a bomb went off, scatter shields are a must and even those can be compromised. it's sobering to see a 0.250" steel plate sheared by a 0.015" carbon disk fragment at only 8krpm.

    then you also have the imbalance issue, they calculate a rotating mass of 300kg with an imbalance of 10kg. with a continual reference to automotive crankshaft balancing, not the same thing I'd say, the crankshaft is not rotating in a constant fashion but oscillates back and forth from the harmonics of the firing order. the flywheel would be a better reference and an imbalance there is a bomb with a lit fuse.

    I can't find rpm data in the proposal, I may have missed that. I do hope they are using a spun disk formed cylinder and not a seamed or extrusion as the grain structure will not take those pressures and temps to satisfy safety. bolts of 316ss will be problem if not addressed, expansion coefficient where the aluminum is going to creep and the joint will fail. it'll need spring washers to offset this difference.

    the use of mineral oil for the sodium raises the question of oil shear at the temps they are talking about, nothing there to say if they've accounted for it. and the bulk of the equations deal with a uniform mass in rotation. I'm familiar with fluid filled rotating assy. and depending upon the viscosity it is not uniform in balance unless the fluid is in uniform viscosity and location. with the combination as I read it of oil and sulfur in a solid state is going to introduce imbalance and harmonics that will need to be dealt with. not to mention the idea of breaking the flow with gas jets which is the whole basis of the test.

    stick that thing in a blast chamber and run it, make sure the cameras running!

    I could go on, but it's only my opinion.

    From your post it sounds like you have a coil of one of many iterations of tesla or others. I think the idea of EM and induced anti-gravity isn't going to get you GW's.

    Further how does one measure the wave when it would distort the detectors space time? Am I missing something, I thought a GW would be non-detectable because its a distortion of space time, akin to measuring the event horizon while being in it.
  11. Feb 6, 2010 #10
    ahh found a video of it in motion, it's going much slower than I thought it would.
  12. Feb 6, 2010 #11
    You do realize who Sterling Colgate is right? This guy can build hydrogen bombs I would be shocked if he blew up a dynamo lol.

    He isn't making his dynamo for GW hes trying to make a sustaining EM field from what I understand. My experiment though it cannot detect GW at all, I can study energy transfers that may or may not be enough to set one off... kind of like you can't see the black hole but you can see the stuff falling into it. I want to study transfers of EM energy from one dynamo to the other and the methods of inducing those energy transfers... because GW can use EM energy from that kind of thing.

    I've never heard of GW being undetectable.. just needing stellar scales of like neutron stars to be able to pick em up if at all really... I mean we are dealing with an unproven theory. I don't think the math alone is proof enough myself, I'm still not sold on the standard model anyway lol.
  13. Feb 6, 2010 #12
    honestly no I don't know who Sterling Colgate is. I wasn't trying to say it would not work, just that at high speeds there are concerns, further reading on the site and the proposals shows that the review committee had the exact same concerns over construction and containment failure.

    even the group is concerned to where it will be tested in an open air bomb range as the potential catastrophic failure could generate a substantial blast.
  14. Feb 6, 2010 #13
    lol what kind of blast would a dynamo make I wonder.

    But I wanted to tell ya that I didn't like how its kind of dependant on lots of things. It seems to me I would make one that could be put in different configurations. I wish he would use some imagination and use different liquids.

    I mean we are talking about Los Alamos here... they should me spinning up liquid hydrogen in my opinion.

    Madhatter may I send you my papers on this??? I"d like your input into the other stuff he sent me to look at. You seem to grasp this stuff real good I could use your take on a few questions i got.

    P.S. Stirling Colgate was the king of nuclear bombs during the 50's and 60's


    I"m framing the letter he sent me lol. I still can't get used to the internet making it so much easier to write famous ppl and get replies.
    Last edited: Feb 6, 2010
  15. Feb 6, 2010 #14
    the 'blast' from the dynamo would be the combined centrifugal and internal pressures they are proposing to run, along with the feature of atomized sulfur and high probability of ignition if containment is lost.

    I'm not knocking Colgate here he could be the best metallurgist and machinist around. I'm coming from the trenches where my dad who was a tool & die maker for aeronautical and petrochemical industry for 30yrs. BIG gap between the engineers and machinist doing to work. I see it as, the math and engineering is the first step in what to expect but the actual physical build constraints and tolerances with material imperfections. there is a reason some parts get magnifluxed and xray'd after machining.

    Im my opinion the testing rig should be tested under operating parameters before the test is carried out to deal with anomalies and possible failures the original scope might have missed. It would help factor out any unwanted test apparatus induced results. hopefully that made some sense.
  16. Feb 6, 2010 #15
    well man I think you will agree, this is an area where standard model physics is just dabbling in. Most of the predictions thus far have been incorrect because of parameters that are unforseable.

    But you are correct about gaps between the scientists/engineers/ and machinists. Myself I am a machinist with a little bit of engineer. I fabricate lots of stuff just for the heck of it. I think their predictions are going to be wrong on most issues.

    But I don't doubt that it may blow up... I think they may record stuff that isn't anticipated as well.

    What do you think about the possibility of a self sustaining EM field?
  17. Feb 7, 2010 #16
    Let me expand on this, from the POV of a man who has SEEN a moderately energetic flywheel explode. Yes. EXPLODE. Even if nothing happens but fragmentation of the device, that shrapnel can have one hell of a lot of kinetic energy. Every impact of a piece of the device will result in either perforation or a heavy impact. The rapidly expanding flywheel, or dynamo also creates a shockwave. In short, store energy in powder, or a wheel, or a turbine or a dynamo... catastrophic release is ALWAYS BAD. Remember that shrapnel is the major danger in explosions (unless you're tragically close to them), along with fire, hearing loss, etc.

    What kind of blast would you get from a dynamo? How many dynamo slivers moving VERY quickly does it take blind or lobotomize you?

    EDIT: Btw... remember that the people who built the original hydrogen bombs were off by a few megatons. ;)
  18. Feb 7, 2010 #17
    Aww come on guys. Your calling that a dangerous explosion? Don't get me wrong.. shrapnel and molten sodium flying around sounds interesting the possibility of a shockwave doesn't impress me though. Now I've not built a dynamo.. YET, well I don't count the 1 foot model I have. And I still can't understand those equations yet. But one thing I do know besides hacking RF is explosives. I was a blaster in an underground limestone mine for about 1 year, what you describe sounds like 1/2 stick of dynamite or maybe a few coils of primer cord. I've been 1000 ft. from 2,200 pound of ammonia nitrate going off. In a full day we would set off 4-5k lbs of that stuff, when you tell me explosion I"m thinking need to be 1/2 mile away or more. I thought you guys were talking about vaporizing stuff. I'm going to ask him though about the risk of explosion and how big a yield we're talking here.

    What is releasing the energy? I don't think his RPMS are high enough to destabilize the sodium. If anything happens I thought the machine might come apart at the seams. I mean I know this guy is 84 yrs old... but guys this is Los Alamos. They will probably have the thing in a bomb shelter. And I couldn't even imagine the tolerances on the machining... I know I wouldn't get that contract. I wonder what kind of speed he'll be pushing at max though.

    Hey man have you made any sense of those papers yet?
  19. Feb 7, 2010 #18
    Let me ask you a very serious question: Why is a fragmentation grenade so deadly? Is it the strength of the explosion, or the nature of shrapnel? An exploding dynamo of this type that experienced primary structural failure (coming apart at the seams as you say) would probably undergo one or two blasts. First the kinetic energy in the shrapnel that initially blows apart is going to be HUGE ("the 'blast' from the dynamo would be the combined centrifugal and internal pressures they are proposing to run, along with the feature of atomized sulfur and high probability of ignition if containment is lost.").

    Second, the sodium and atomized sulpher means you'll have atomized sulpher and hydrogen gas upon release, with the sodium acting as a self-ingitor for its own hydrogen. In this scenario even a partial failure results in a second stage explosion that will blow the apparatus apart (hydrogen and sulpher, so bad only if you're RIGHT there, so relatively safe)... but again, you'd probably have total failure of the dynamo and shrapnel with ridiculous kinetic energy.

    Presumably Los Alamos would deploy this on a bomb range and no LOS would be allowed; only cameras and instrumentation. That's a pretty extreme experiment if you're not TRYING to blow something to pieces. Then again, you never know just what ballistic trajectories so much shrapnel is going to take.

    EDIT: Remember the grenade; the very nature (tough pieces that have mass, become hot and semi-molten) of the casing is what makes it so deadly. Make this dynamo heavier and such, and all you're doing is adding shrapnel.
  20. Feb 7, 2010 #19
    I imagined the failure of a machine that is supposed to be simulating the accretion disc of a black hole as a mini big bang lol. I guess its all those big words I don't understand I'm expecting a little much.

    But heck anything that explodes is entertaining even if its a lil cherry bomb I still wanna see it!

    I didn't realize there would be hydrogen gas, thats very explosive stuff. Underground once when I came up on one of our little scoops that runs on 460 DCV, somebody had left the battery covers down and had the charger hooked up. I turned around for a sec and heard a BOOM and the place was daylight for second, when my buddy threw back the lid it sparked. He knew better really, charging batteries give off hydrogen gas and can be VERY explosive. He blew an eardrum and singed his hair and his pride but he was very lucky.

    Thanks for the information, I'd love to watch this thing run.
  21. Feb 7, 2010 #20
    Well let me clarify here, before I become a liar! Metallic sodiom reacts with water (among other things) and in the intense heat, hydrogen is produced... and usually ignited. It's a classic trick in (some age school, I don't know anymore, high school for me) to take slivers of sodium or magnesium/potassium... which is preserved in mineral oil or kerosene to protect it from air and water.... and do just that.

    Spark, spark, smoke, boom!.

    So, there is no H in the machine that I can see, but the sodium would produce a lot of it, and while I don't know what exactly happens when atomized sulpher, HOT Na, and all of that dynamic energy goes "poof".

    Are you more afriad of a HUGE bomb that goes as planned, or a cherry bomb that does nothing after you light it? Which is more likely to take off a hand? As a man who has been on a work-site, I don't need to tell you. So yeah, this is not a thermonuclear device or anything so grand, but as physics experiments at low energies goes... it's pretty racey! ;)

    Edit: I would love to see it run too... on a live video feed out of line of sight. :rofl:
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